Norwegian patent 155 826 discloses an umbilical capable of transporting hydraulic fluids, chemicals, electric and optical signals and electrical power. The conduit for chemical transport is usually placed in the center, while those for electrical signals an power and the hydraulic pipes are placed peripherally around the central element or core element. The peripherally situated elements are wound into a helix around the central pipe. Each element is free to move longitudinally in relation to the other elements. The cable core is wrapped with a band, and the outer sheath is a thermoplastic layer extruded onto the cable core.
The core element may be a metal tube for conducting a liquid or may be an electrical cable for transmission of power or signals. As a metal tube it may be used, e. g. for injection of methanol into a drilling well.
The outer sheath may consist of polyethylene or polyurethane that is extruded onto the cable in a final step.
European patent specification 627 027 discloses a method and apparatus for manufacturing and laying out an umbilical. The umbilical consists of a central element a tube or several cables—with tubes or cables wound onto the central element. Filler elements are situated around and between the conduits or cables. The filler elements have voids designed to reduce weight and use of material. In addition, precise profile dimensions require uniform material thickness, necessitating the voids. The filler elements may consist of extruded polyvinylchloride profiles.
One drawback of the known umbilicals is that the voids act as buoyancy.